Ds-cdma integration spreading coherent receiver

ABSTRACT

The Spread Spectrum integration coherent receiver of the invention employs a time division multiplexing correlator bank and thus obtained coherent channel evaluator as a core. The receiver can execute initial PN synchronization, RAKE diversity coherent combination, AFC and adjacent cell search and combination receipt, and soft handoff. Further, “part capture in parallel based on slide energy window” and “tracking loop based on energy window barycenter” are introduced into the receiver of the invention, thereby simplifying the structure of the RAKE receiver. The receiver is capable of overcoming multipath fading, ensuring the RAKE receipt performance.

FIELD OF THE INVENTION

[0001] The present invention relates to a CDMA (code division multipleaccess) cellular communication system.

BACKGROUND OF THE INVENTION

[0002] Mobile communication techniques have become a widely usedcommunication manner for their advantages such as flexibility andconvenience since 1980s. In a lot of mobile communication standards,CDMA cellular communication technique shows great potential for itsfeatures associated with large capacity, simple frequency planning, goodcommunication quality and small electromagnetic interference. IS-95 CDMAcellular communication system proposed by Qualcomm Inc. and rapidlydeveloped all over the world uses this CDMA cellular communicationtechnique. Several candidate schemes of the third generation of digitalcellular communication system are established on the basis of CDMAtechniques.

[0003] Multipath fading which causes serious multipath interferenceexists in a mobile communication system. In general, it is necessary toreceive pilot signals with confirmation information so as to evaluatethe amplitude and phase information of multipath signals, and it ispossible to achieve multipath diversity and coherent reception. Acoherent spread spectrum receiver which performs diversity process isreferred to as RAKE coherent receiver. RAKE coherent receiver cancorrect phases of a plurality of singlepath signals which carry sameinformation and are independence from one another in fading features,and perform maximal combination to overcome multipath fading and improvereceived signal-to-interference ratio.

[0004] To achieve RAKE reception function, Synchronizing local spreadspectrum sequence (PN code) with received signal is necessary. Thesynchronization is achieved by acquiring and tracking steps. Theacquiring step acquires a pilot channel and confirms that initialsynchronization (coars synchronization) of PN code is complete. Thecombination of these two steps provides PN code and accurate localtiming required for RAKE receiver.

[0005] Mobile communication spread spectrum receivers in CDMA cellularcommunication system have capabilities of diversity combination receiptto achieve soft handoff so as to improve receiving performance atboundaries of cells.

[0006] CDMA receivers have large local oscillation frequency-offset inturn-on losing lock state due to the limit of cost. An automaticfrequency correction (AFC) function is introduced into the receivers sothat the RAKE receivers can operate normally in large local oscillationfrequency-offset state.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to providedirect sequence spread spectrum integration coherent receiver designedwith a “energy window barycenter” method to overcome the disadvantagesdue to the non-determinacy of multipath signals in mobile communication.The receiver according to the invention can process multipath energywindow in parallel, and execute the operations such as synchronizationtrack, RAKE diversity coherent combination, AFC and adjacent cell searchand combination receipt, and soft handoff, there by improving theperformance of CDMA spread spectrum receivers, and reducing hardware.

[0008] The present invention is implemented by the technical solutiondescribed later.

[0009] The Spread Spectrum integration coherent receiver according tothe invention uses a time division multiplexed correlator bank and thusobtained coherent channel evaluator as a core. Further, the receiver canexecute initial PN synchronization, RAKE diversity coherent combination,AFC and adjacent cell search and combination receipt, and soft handoff.Furthermore, “partially acquiring in parallel based on sliding energywindow” and “tracking loop based on energy window barycenter” areintroduced into the receiver according to this invention. Unlikeprocessing a singlepath as disclosed in patents issued to Qualcomm Inc.,the receiver according to the present invention can solve the problemscaused by multipath fading, ensure the RAKE receipt performance andsimplify the structure of the RAKE receiver.

[0010] According to an aspect of the invention, it provides a directsequence spread spectrum/CDMA integration spread spectrum coherentreceiver comprising a state control means for receiving controlinformation from a CPU (center processor unit), generating controlinformation used for operating each of units, recording the generatingunit for receiving a external clock, generating CPU interruption signalsrequired for entire system, timing clock and time sequence by dividingfrequency and counting, and for adjusting the timing based on a PN codetracking unit and the state control unit; a correlator bank forperforming effective correlating integration by time divisionmultiplexing one complex correlator to form equivalent correlators; apost correlation data processing unit for receiving the output from oneof correlator in the correlation bank, processing the data included inthe output from the correlator, performing initial acquisition, adjacentcell search, selection of effective multipath based on the energy windowaccording to the control information from. state control unit; a PN codetracking unit for receiving a channel evaluation relating to effectivemultipath of pilot channel from the post correlation data processingunit, calculating a energy window barycenter and a loop filter to obtaina mode value for a variable mode counter, and sending the mode value tothe timing generating unit to finely adjust the PN code generationclock, thereby adjusting local PN code phase; and an automatic frequencycorrection (AFC) loop calculating unit for performing frequency errorevaluation and loop filter calculation based on the informationassociated with effective multipath of the pilot channle, and sendingthe obtained result to a controllable frequency reference unit.

[0011] The principle of the invention will be discussed.

[0012] The algorithm executed by the CDMA spreading coherent receiver ofthe invention includes parts of channel parameter evaluation, maximalratio combination, and associated initial PN acquisition, track, AFC,adjacent cell search, hand-off, and macro-diversity. Each of parts isdescribed as follows.

[0013] 1. Channel Parameter Evaluation

[0014] A pilot channel in CDMA system is used for transferring a pilotsequence known in advance which may provide a system timing, extractcarriers, evaluate channels, and execute hand-off, etc. The equivalentbaseband receiving signals may be expressed as shown in equation (1)when the system simultaneously transmits signals through a plurality ofchannels, $\begin{matrix}{{r(t)} = {{\sum\limits_{n}{c_{n} \cdot {\sum\limits_{i}{s_{i}\left( {t - {n/W}} \right)}}}} + {z(t)}}} & (1)\end{matrix}$

[0015] wherein s_(I)(t) represents the signs and equivalent basebandsignals transmitted through with code division channel in downstreamchannels. The term of i=0 corresponds to the pilot channel. z(t) iscomplex White Gaussian noise of zero average value, c_(n) is a fadingfactor of nth path of the channels. The purpose for evaluating channelparameter is to evaluate channel fading factor c_(n) based on thereceived signals r(t) and the known pilot sequence s_(o)(t).

[0016] It is assumed that frequency selectivity slow fading channelmodel is used as a mobile channel, c_(n) is then approximate to aconstant within the channel evaluation region. The evaluation value ofc_(n) is given as follow: $\begin{matrix}{\overset{\_}{c_{n}} = {{\frac{1}{{NE}_{c}}{\int_{0}^{{NT}_{c}}{{{r\left( {t - {nT}_{c}} \right)} \cdot {s_{0}^{*}(t)}}{t}}}} = {c_{n} + N_{a} + N_{c} + N_{z}}}} & (2)\end{matrix}$

[0017] wherein N_(a), N_(c), and N_(z) are th outputs caused bymultipath interference, multipl access interference and white noisepassed through a correlator due to the non-ideal correlationcharacteristic, T_(c) is a time width of one chip, NT_(c) is anintegration region of a channel evaluation, and E_(c) is energytransmitted through a pilot channel within one chip.

[0018] 2. Maximal Ratio Combination

[0019] After obtaining the channel parameter evaluation values for eachof paths, other channels carrying data are coherently demodulated. Tothis end, it only needs to despread each of paths of other channels. Thechannel evaluation parameter c_(n) obtained by using equation (2)weights the amplitude of despreaded results for each of paths andcorrects the phase thereof to make the despreaded results in phasecombine. This processing is referring to as maximal ratio combination.The equation will be described in detail as follows: $\begin{matrix}{{\overset{\_}{d}}_{i} = {\frac{1}{E_{b}}{\sum\limits_{n}{\overset{\_}{c_{n}^{*}}{\int_{0}^{T_{s}}{{{r\left( {t - {nT}_{c}} \right)} \cdot {s_{i}^{*}(t)}}{t}}}}}}} & (3)\end{matrix}$

[0020] wherein {overscore (d)}_(i) is data transmitted on with channelcarrying data, T_(s) is a sustaining interval of data, {overscore(c)}_(n) and {overscore (c)}_(n) is a conjugate pair. In practice, it isnot that all paths, which may be identified by RAKE receiver, haveeffective signal components. Comparing {overscore (c)}_(n) with athreshold, only the multipath components which {overscore (c)}_(n) arehigher than the threshold are combined.

[0021] 3. Local Pilot Signal Restore

[0022] In foregoing channel evaluation, it is necessary to know pilotsignals s_(o)(t). Therefore, the pilot signals s_(o)(t) are restored inlocal based on the received signals r(t). Restoring the pilot signalss_(o)(t) comprises acquiring step which performs coarselysynchronization (initial synchronization) and tracking step whichperforms fine synchronization. Acquiring pilot signals is also referredto as PN codes acquisition. Tracking pilot signals is also referred toas PN codes track. In this invention, acquiring pilot signals isperformed by using initial synchronization method of CDMA cellularsystem based on the maximal energy window. Tracking pilot signals isperformed by using pilot signal track method based on multipath channelenergy window barycenter tracking loop.

[0023] Next, the principle of initial synchronization in CDMA cellularsystem based on the maximal energy window is described.

[0024] In initial synchronization stage of a CDMA receiver, the phaseinformation of received signals can not be known. It is necessary toevaluate multipath fading channels in fraction intervals, and tryevaluation using local pilot sequence (PN code) with different phase. Inthis case, following equation (4) can be derived from equation (2).$\begin{matrix}{\begin{matrix}{{{{\overset{\_}{c}}_{n,m}(k)} = {\frac{1}{{NE}_{c}}{\int_{0}^{{NT}_{c}}{{{r\left( {t - {nT}_{c} - {{mT}_{c}/M}} \right)} \cdot {s_{0}^{*}\left( {t - {{kT}_{c}/M}} \right)}}{t}}}}},} \\{{m = 0},1,{{\text{?}\quad M} - 1}}\end{matrix}{\text{?}\text{indicates text missing or illegible when filed}}} & (4)\end{matrix}$

[0025] wherein T_(c)/M is fraction sampling intervals, k is a possiblecertain phase parameter of the local pilot PN sequence.

[0026] The effective distribution range of channel fading factor c_(n)in equation (1) is defined as energy distribution window of multipathsignal (hereinafter is referred to as multipath energy window). The sizeof the window may be determined by time-delay extend range of multipathchannels. For the sake of simplifying discussion, the effectivedistribution range of c_(n) may be set to n∈[−L₁,L₂]. The size of thewindow in multipath fading circumstances may be set differently fordifferent areas, for example, 3 μs for cities, 6 μs for countries, and15 μs for mountain areas. The size of window is associated with thecircumstances where the cellular communication system is located, and isregardless of the used frequency band. The size of multipath energywindow may be selected according to the maximal likelihood value, forexample, no more than 30 μs, and then the value of L=L₂−L₁+1 is not morethan 30 μs/T_(c) so that a spread spectrum receiver can be used invarious circumstances.

[0027] In a multipath energy window, not all signal arrival paths areeffective. To this end, a threshold may be set to judge the signalenergy (i.e., intensity of c_(n)) for each of paths in the window. Asignal arrival path is judged as effective path when the signal energyis larger than the threshold. Otherwise, the path is judged as a pureinterference path. To avoid the degradation of the performance, thecalculation is not applied to all pure interference paths. The thresholdis set slightly larger than the side lobe value of a pilot signal (PNcode) partial correlation value.

[0028] To obtain sufficient acquisition precision, a receiver samplesthe received signals using over-sampling technique. The sampling rate isM times the chip rate of PN code. Assuming the length of PN coderequired for synchronizing is p, the PN code acquiring method of theinvention selects a phase from M×P possible PN code phases, and maximizethe multipath energy contained in the multipath energy window.

[0029] According to above concept of multipath energy window, themultipath energy window which the phase of local PN code is k is definedas follow: $\begin{matrix}{{E_{win}(k)} = {\sum\limits_{n = {- L_{1}}}^{L_{2}}{\sum\limits_{m = 0}^{M - 1}{{{\overset{\_}{c}}_{n,m}(k)}}^{2}}}} & (5)\end{matrix}$

[0030] the acquiring method based on multipath energy window is theredescribed as the selection of a value k which makes following equation(6) have a maximal value from all possible values k of local PN codephase:

[0031] $\begin{matrix}{\max\limits_{k}\quad {E_{win}(k)}} & (6)\end{matrix}$

[0032] On the other hand, it can be seen from equation (4), themultipath energy window calculation as shown in equation (5) existsfollowing derivative relationship associated with a sliding window:

E _(wln)(k+1)=E _(wln)(k)−|{overscore (c)}L ₂ M−1(k)|² +|{overscore(c)}L ₁.0 (k+1)|²  (7)

[0033] Thus, Initial synchronization calculation can be greatlysimplified.

[0034] The method of searching adjacent cells is similar with theinitial synchronization method of PN code except for that the PN codeutilized in the equation is a pilot signal sequence in a certainadjacent cell, the region to be searched is a designating region inadvance by a base station, but not all possible phases of PN codes.

[0035] Next, the principle of pilot channel tracking method based on themultipath energy window barycenter tracking loop is described.

[0036] If K denotes the evaluated result of kth channel, the barycenterof corresponding multipath energy window is given bycg(k)=cg_(w)(k)/cg_(s)(k), wherein cg_(w)(k) and cg_(s)(k) arecalculated as follows: $\begin{matrix}\begin{matrix}{{{{cg}_{w}(k)} = {\sum\limits_{n}{n{{\overset{\_}{c_{n}}(k)}}^{2}}}},} & {{{cg}_{s}(k)} = {\sum\limits_{n}{{\overset{\_}{c_{n}}(k)}}^{2}}}\end{matrix} & (8)\end{matrix}$

[0037] wherein n corresponds to the position where the multipath fadingfactor {overscore (c)}_(n)(k) locates in multipath energy window. Itshould be noted that each of {overscore (c)}_(n)(k) S to be calculatedin equation (8) is an effective signal arrival path which is large thandesignated threshold.

[0038] PN code tracking loop for multipath energy window barycenter isdesigned such that the target position of a multipath energy windowbarycenter is set to cg_(target) so that the PN code phase of thereceiver can be adjusted by detecting the difference between themultipath energy window barycenter r value cg(k) and cg_(target) toreduce the difference. For simplifying the calculation, it s assumedthat cg_(target) is set to zero, the phase adjustment of local PN codecan be then performed by simply judging the polarity of cg_(w)(k), butnot need to calculate cg_(s)(k) and cg(k).

[0039] To avoid incorrect adjustment due to the random changes ofmultipath fading signals and channel evaluation errors, the barycenterevaluating value calculated by equation (3) is smoothly filtered.Assuming the smoothly filtered evaluating value is cg_(w)(k), theadjusting operation can generalized to:

let the phase of local PN code lead δ if {overscore (cg_(w)(k))}>0

let the phase of local PN code lag δ if {overscore (cg_(w)(k))}<0

let the phase of local PN code hold if {overscore (cg_(w)(k))}=0  (9)

[0040] The local PN code phase adjusting unit performs the operation asshown in equation (9). According to an embodiment of the presentinversion, the local PN code phase adjustment is executed by finelyadjusting the transmitting clock of local PN code. FIG. 2 illustrates anoperation flowchart of the method according to the invention. In FIG. 2,the PN code clock is generated by courting the frequency division of amultiple times (M times) the external clock. A variable mode counterfinely adjusts the chip clock. The mode value of the counter is M−1ifthe {overscore (cg_(w)(k))} is positive. The mode value is M+1 if the{overscore (cg_(w)(k))} is negative. Otherwise, the mode value of thecounter is M. In this way, the PN code phase can be adjusted as shown inequation (9), and the phase difference of fine adjustment is δ=T_(c)/M,wherein M may be 32 or 64 to measure the adjustment accuracy enough.

[0041] 4. Automatic Frequency Correction (AFC)

[0042] In practice, the stability of initial frequency in a mobileterminal is limited to about 1 ppm because of the restrict by volume andcost, etc. This results in there are approximate several hundred Hz toseveral KHz frequency difference between a base station and a mobileterminal. Therefore, it is necessary to introduce an automatic frequencycorrection (AFC) function into mobile terminals, thereby preventing thedegradation of the system performance. In view of the effects due to thefrequency difference between transmitting side and receiving side, theequivalent baseband model in equation (1) can be depicted as equation(10): $\begin{matrix}{{r(t)} = {{\sum\limits_{n}{{c_{n} \cdot ^{j\quad \Delta \quad \omega_{c}t}}{\sum\limits_{l}{s_{i}\left( {t - {n/W}} \right)}}}} + {z(t)}}} & (10)\end{matrix}$

[0043] wherein Δω_(c) is the frequency difference between a transmittingside and a receiving side. The channel evaluation as shown in equation(2) can be modified as shown in equation (11): $\begin{matrix}\begin{matrix}{\overset{\_}{c_{n}} = {\frac{1}{{NE}_{c}}{\int_{0}^{{NT}_{c}}{{{r\left( {t - {nT}_{c}} \right)} \cdot {s_{0}^{*}(t)}}{t}}}}} \\{= {{c_{n} \cdot \left\{ {^{j\quad \Delta \quad \omega_{c}{{NT}_{c}/2}}\frac{\sin \left( {\Delta \quad \omega_{c}{{NT}_{c}/2}} \right)}{\Delta \quad \omega_{c}{{NT}_{c}/2}}} \right\}} + N_{a} + N_{c} + N_{z}}} \\{\cong {{c_{n}^{j\quad \Delta \quad \omega_{c}{{NT}_{c}/2}}} + N_{a} + N_{c} + N_{z}}}\end{matrix} & (11)\end{matrix}$

[0044] wherein assuming Δω_(c)NT_(c)/2<<1. The evaluation value ofΔω_(c) is obtained by using the evaluation value of {overscore (c)}_(n)in two sequential regions t∈[0, NT_(c)] and t∈[(N+1)T_(c),(2N+1)T_(c)],and assuming that c_(n) does not charge in the two sequential regions.The local oscillator source of a mobile terminal can be adjusted byusing the obtained evaluation, thereby achieving AFC function.

[0045] 5. Soft Hand-off and Macro-diversity

[0046] Soft hand-off and macro-diversity are essential function for aCDMA cellular communication system. A mobile terminal detects theintensity of signals from adjacent base stations when the mobileterminal enters boundaries of two or more adjacent cells. When theintensity of the signal from a certain base station is larger than apredetermining value, the mobile terminal enters into macro-diversitystate, communicates with two or more base stations simultaneously, andcombines the same data transmitted from the two or more base stations toimprove the performance of the mobile terminal when it is in boundariesof cells.

[0047] The detection of signal intensity, which is required by softhand-off, from adjacent base stations can be achieved by evaluating theintensity of pilot channel transmitted from the adjacent base stations.This can be accomplished by replacing the pilot signals in equation (2)with the pilot signals from the adjacent base stations and performingchannel evaluation on a certain multipath distributing region. When theevaluated pilot signals are larger than a predetermined intensity, themobile terminal informs the base station with which is communicating ofthe event and prepares to enter into a macro-diversity state.

[0048] The signals from a plurality of base stations need to be receivedand combined when the mobile terminal enters into a macro-diversitystate. This can be accomplished by replacing the spread spectrum signals(sequence) in equation (3) with the spread spectrum signals transmittedfrom the adjacent base stations and simultaneously receiving data fromtwo or more base stations in macro-diversity state, and then performingpost combination after aligning in time

THE ADVANTAGES OF THE INVENTION

[0049] The present invention provides a initial synchronization methodbased on the energy window and PN code track method based on the energywindow barycenter with respect to the random change characteristic inmultipath fading circumstances. This method does not need toindividually process each delay path. Therefore, the stability of aspread spectrum receiver in multipath fading circumstances is improved.This invention also induce the operation which need to be performed by aspread spectrum receiver into equations (2) (or (5)) and equation (3).Further, this invention provides a design method used for spreadspectrum receivers so that the hardware used in spread spectrumreceivers is greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwith reference to the accompanying drawings, which illustrate examplesof the present invention.

[0051]FIG. 1 schematically illustrates a configuration of a spreadspectrum receiver according to an embodiment of the invention; and

[0052]FIG. 2 schematically illustrates a diagram showing the PN codephase adjustment according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Referring now to the accompanying drawings, there are shownpreferred embodiments of the invention. As described above, each ofparts in a spread spectrum receiver is based upon equations 3 and 11 (orequation 2). The spread spectrum receiver can accomplish functions suchas initial synchronization of the pilot channel, track and channelevaluation, multipath maximal ratio combination, AFC, adjacent cellsearch, hand-off, and macro-diversity. Accordingly, this inventionprovides the arrangement of a CDMA spread spectrum receiver.

[0054] A preferred embodiment of the invention will be discussed withreference to FIG. 1.

[0055] The CDMA spread spectrum receiver according to the inventioncomprises a state control unit (FSM_CONTROL), a timing generating unit(SYS_CLK), a data delay line unit (DELAY_LINE), a correlator bank(CORRELATOR_BANK), a post correlation data processing unit (POST_CPRR),a RAKE combining unit (RAKE_COMB), a post combining unit (POST_COMB), aPN code generating and sliding unit (PN_GROUP), a WALSH functiongenerating unit (WALSH_GEN), an AFC loop calculating unit (AFC_LOOP),and a PN code tracking unit. The functions and operation of each of theunits are described as follows. 1. State Control Unit (FSM_CONTROL)

[0056] The state control unit includes a CPU interface block, A receiverstate transformation control (TOP_FSM) block, and a unit state controlsignal generating (DOWN_FSM) block. The state control unit interactswith the CPU, which is controlled by baseband, of information, receivescontrol information from the CPU, generates control information used foroperating state transformation of each of units, records the operationstates of each of the units and reports the states to the CPU. The CPUinterface has a build-in RAM. The storage capacity of the RAM may bedetermined as desired, for example, 64×8 bits. The CPU read/writes theRAM in the manner of interrupting poll, interacts with the statetransformation control block of the receiver to transfer information.TOP_FSM scans the RAM in the period of interrupting signals (e.g., 26.27ms, 20 ms, or 10 ms depended upon the application or the state of areceiver) and receives control information from the CPU (e.g., acquiringstate, searching state, receiving states of various code channel) andsystem parameters (e.g., the number of code channel, spread spectrumrate, searching region, and frame-offset, etc.) required for arrangingoperation so as to determine next operation state. Further, the TOP_FSMinstructs the DOWN_FSM to generate control signals for other units. Theinformation indicating that state transformation is complete istransferred to the RAM unit so that the CPU can obtain correspondingfeedback information.

[0057] 2. Timing Generating Unit (SYS_CLK)

[0058] The timing generating unit receives external clocks (in general,16 times or 32 times the spread spectrum sequence chip rate), generatesCPU interruption signals required for entire system, timing clock andtime sequence by dividing frequency and counting, and adjusts the timingbased on a PN code tracking unit and the state control unit. The timinggenerating unit generates N sets of timing signals dependent on thereceiving links of each of base stations to support macro-diversity ofat most N base stations. Further, The timing generating unit tracks thetiming in accordance with the channel evaluation of respective basestations and the result of the tracking unit. In the process ofmacro-diversity, the relative time-delay changes of respective receivinglinks are measured and reported to the CPU. The CPU controls thepost-control unit to perform macro-diversity function after aligning thetime-delay of respective links.

[0059] 3. Data Delay Line Unit (DELAY_LINE)

[0060] The data delay line unit comprises four sets of RAMs, whichstorage capacity is, for example, 18×6 bits, or D flip-flops. The datadelay line unit samples 4 times the input data and outputs 72 delay tapswith ¼ chip interval. The output data is provides to a correlator bankunit.

[0061] 4. Correlator Bank Unit

[0062] The correlator bank comprises four banks of correlators. Eachbank of correlators perform effective correlation integration 31 timesby time division multiplexing one complex correlator (multiplexing with32 times the chip rate), thereby forming 31×4 equivalent correlators sumtotal. Each of equivalent correlators performs the calculation as shownin equations 3 and 5 (or 2) with the chip interval. Correlators in eachbank are numbered 0 to 30 in accordance with the sequence of timedivision multiplexing. Correlators 0-17 in each bank (sum to 4×18equivalent correlators in four banks) are used for evaluating multipathchannel in parallel. A following POST_CORR unit performs acquisition,adjacent cell search and effective selection etc. on the evaluatedresults. Correlators 8-30 in each bank are used for evaluating channelsof effective paths from base stations and despread data carried on datachannel. Marco-diversities of three base stations are supported.

[0063] The configuration of a correlator bank may be arranged as desiredso as to easily support different system standard.

[0064] 5. Post Correlation Data Processing Unit (POST_CORR)

[0065] The post correlation data processing unit receives the outputfrom the correlators in correlation banks, and processes the dataincluded in the output from the correlators, performs initialacquisition, adjacent cell search, selection of effective multipathbased on the energy window according to the control signals fromFSM_CONTROL unit. The processed results are provided to the PN codetracking unit, AFC loop unit and the state control unit.

[0066] 6. RAKE Combining Unit (RAKE_COMB)

[0067] The RAKE combining unit receives the channel evaluated resultsfrom POST_CORR unit and decorrelates the data stream, and combines(equation 3) the effective multipath according to the control signalsfrom FSM_CONTROL unit. The results are provided to a post combiningunit.

[0068] 7. Post Combining Unit (POST_COMB)

[0069] The post combining unit receives multipath combining results fromRAKE_COMB unit, and determines whether or not to perform macro-diversityof a plurality of base stations according to the control signals fromFSM_CONTROL unit. If macro-diversity is necessary, the post combiningunit delays paths based on the time-delay difference of respective basestations provided by the CPU so as to align the paths to each other intime, and performs macro-diversity of a plurality of base stations.

[0070] 8. PN Code Generating and Sliding Control Unit (PN_GROUP)

[0071] Five groups of PN codes are provided, wherein three of them areused for the despread data of three base stations. One of rest groups ofPN codes is used for adjacent cell, the other group of PN codes is usedfor transmitter. The PN code used for adjacent cell search depends onmain receiving links. The instantaneous process in PN code slidingprocess is shield to avoid confusing the demodulation results of thereceiver. The timing of PN code used for transmitters depends on thetiming of base stations which have been acquired when a receiver isturned on. When a link is released, the PN code of the link shouldsynchronize with the PN code of main receiving link so that the relativereference positions among PN codes are in known state.

[0072] 9. Walsh Function Generating Unit (WALSH_GEN)

[0073] The Walsh function generating unit is controlled by the slatecontrol unit (FSM_CONTROL) and the timing generating unit (SYS_CLK), andgenerates three Walsh sequences depended on respective links.

[0074] 10. AFC Loop Calculating Unit (AFC_LOOP)

[0075] The AFC loop calculating unit evaluates frequency error andcalculates loop filter based on the effective multipath information ofpilot channel provided from FSM_CONTROL and SYS_CLK, and send the resultto a controllable frequency reference unit.

[0076] 11. PN Code Tracking Unit (CG_LOOP TRACKING)

[0077] The PN code tracking unit receives the effective multipathchannel evaluation of pilot channel from the post correlation dataprocessing unit, calculates the energy window barycenter and loopfilter, and obtains a mode value of a variable mode counter. The resultis sent to the SYS_CLK unit to finely adjust the timing of local PNcode, thereby adjusting the phase of local PN code.

[0078] Next, the operation of main function of CDMA spread spectrumreceiver will be described.

[0079] 1. Initial Acquisition Function

[0080] The CPU writes initial acquisition state control word intoFSM_CONTROL unit. The control word has initial acquisition controlcommand, the length of search region and the number of PN code used forsliding correlation, and integrating periods etc. When the startposition of next frame is arrived at, the TOP_FSM block receives theinitial acquisition information through the interface. Then, the TOP_FSMblock initializes the acquisition, informs the DOWN_FSM block of thegeneration of PN code state control signal, the integrating periodcontrol signal of the CORRELATOR_BANK unit and the POST_CORR unitacquisition state control word etc.

[0081] The PN_GROUP unit periodically slides PN code after receiving thenumber of the used PN code and the number of sliding chips every time.The output of the PN_GROUP unit jumps 16 chips every integrating periodand sends to the CORRELATOR_BANK unit.

[0082] The CORRELATOR_BANK unit receives baseband sampling input signalsand PN code signals as described above. Then, the CORRELATOR_BANK unitperiodically performs correlation calculation as shown in equation 2 or5 based on the control signals from the DOWN_FSM block. Forty-sixmultipath channel evaluations with ¼ chip interval are obtained, and theresults are sent to the POST_CORR unit for followed process.

[0083] The POST_CORR unit receives the parallel integration output fromthe CORRELATOR_BANK unit, and calculates the sliding energy window andcompares it with a maximal value according to the control signals fromthe DOWN_FSM block.

[0084] Repeating above processes, the DOWN_FSM block send acquisitionstop signal when the length of search period designated by the CPU isover. The POST_CORR unit sends the position and energy value of themaximal sliding energy window to the FSM_CONTROL unit and then read bythe CPU.

[0085] The CPU obtains the position and energy value of the maximalsliding energy window and determines whether the energy is larger thanthe basic energy required for acquisition. If it is positive, the CPUsends the information of sliding PN code to the FSM_CONTROL unit. TheFSM_CONTROL unit controls the corresponding PN code to establish therequired inital sychronization PN code (hereinafter referring to as mainsynchronization code). If it is negative, this acquisition is fail.

[0086] After finishing initial synchronization, the CPU immediatelyinforms the FSM_CONTROL unit to enter synchronization tracking state fitthis time, the CORRELATOR_BANK unit performs correlation calculationbased on the established main synchronization code. The result is sentto the POST_CORR unit. The POST_CORR unit selects effective paths,calculates the barycenter position, and generates a PN fine adjustmentsignals based on the shift of the barycenter. The SYS_CLK unit finelyadjusts chip timing based on the fine adjustment signal to keep thesynchronization of chip timing. Also, the CPU informs the FSM_CONTROLunit to perform AFC operation, and the result is used for adjusting themain reference clock of the RF block in the receiver.

[0087] 2. Data Despread Function

[0088] When the receiver despreads a certain code channel, the CPUwrites state control signals and parameters including the number of acode channel (WALSH sequence number), Integrating length etc. into theFSM_CONTROL unit. The TOP_FSM block reads the information when aninterruption arrives at after the FSM_CONTROL unit receives theinformation from the CPU and informs the DWON_FSM block to generateassociated control signals.

[0089] The PN_GROUP unit provides main PN code used for despread data.

[0090] The WALSH_GEN unit generates associated WALSH sequence number.

[0091] The CORRELATOR_BANK unit receives baseband sampling signals, mainsynchronization PN code and WALSH sequence, and performs integratingoperation as shown in equation 3 based on the integration period controlsignal generated by the DWON_FSM block. At the same time, theCORRELATOR_BANK unit perform channel evaluating operation as shown inequation 5 (performing the evaluation of 4×18 channel parameters everyintegration interval). The POST_CORR unit extracts the result and sendsit to the RAKE_COMB unit.

[0092] The function operation for despreading data, which is executed bythe POST_CORR unit, relates to two aspects. On one hand, the number andposition of the effective multipath is determined according to thereceived pilot signal, and then sent to the CORRELATOR_BANK unit so asto determine the position of despreading data associated with effectivemultipath in next integration interval. On the other hand, the channelparameters of effective multipath are chosen and then sent to RAKE_COMBunit to perform multipath combination.

[0093] The RAKE_COMB unit receives the results of effective multipathparameter evaluation and data despread to combine the maximal ratio, andsend the combining result to a channel decode unit through a parallelinterface.

[0094] 3. Adjacent Cell Search Function

[0095] The process of adjacent cell search function is similar with theprocess of initial acquisition except for that the adjacent cell searchfunction need to be performed along with other functions (for example,data despread function) simultaneously. The regions to be searched arethe local areas designated by CPU.

[0096] 4. Macro-Diversity and Soft Hand-off Function

[0097] The accomplishment of macro-diversity and soft Hand-off is morecomplex than other functions, which includes a macro-diversity preparingstage, a macro-diversity implementing stage, and a macro-diversityremoving stage. In the macro-diversity preparing stage, the operationincludes:

[0098] a. A mobile station searches the pilot signal intensity of eachof base stations in accordance with the requirements of the basestations during the mobile station communicates with a single basestation. When the signal intensity of station reports the base stationof the searching result. After receiving a response from the basestation, the mobile station modifies an active set maintained in themobile station.

[0099] b. The time-delay from each base station to the mobile station iscalculated for the purpose of determining the relationship between signand time-delay of each base station. The calculated time-delay isreported to the CPU and provided to the POST_COMB unit to align thearrival time-delay combined by each base station

[0100] After finishing the macro-diversity preparing stage, the mobilestation enters the macro-diversity implementing stage. The mobilestation searches the changes of signal intensity and the time-delayarrived at the mobile station for each of the base stations in real timewhile it combines a plurality of arrival signals of base stations. Themobile station adjusts the signs and delays of the signals arrived atthe mobile station from each of base stations to ensure receiversynchronously receives signals from a plurality of base stations whilethe mobile station measures the intensity of pilot signal from each ofbase stations.

[0101] A T_Drops timer is started when the intensity of pilot signalfrom a certain base station is lower than the threshold. If the timer isexpired, the processing proceeds to the macro-diversity removing stage.

[0102] In macro-diversity removing stage, the mobile station resets alltimings and counts associated with the base stations whichmacro-diversity is to be removed. The PN code timing used inmacro-diversity is restored to the state of synchronizing with a mainbase station. The pilot signal used by the base station is removed fromthe active set.

EXAMPLE

[0103] Next, the implement of the present invention is described with amobile terminal in CDMA 2000 system used as an example. The mobileterminal may be a vehicle mobile station in CDMA 2000 cellular mobilecommunication system fitting Standard 3GPP2 Release A. The spreadspectrum receiving part in the mobile station can be implemented by, forexample, a XC4085xla FPGA chip, a product of Xilinx company. The mainparameters are listed as follows:

[0104] Spreading chip rate is 1.2288 MHz;

[0105] I/Q sampling rate is 4×1.2288 MHz, 6 bits input;

[0106] External clock (EXT_CLK) is 39.3219 MHz;

[0107] Integrating period for channel evaluating is 384 chip intervals(N=384);

[0108] Initial synchronization time is 0.75 s;

[0109] Applicable range of AFC is ±2 KHz;

[0110] Data transformation rate is 19.2 kbps to 307.2 kbps.

[0111] The spread spectrum receiver according to the invention canprovide excellent stability in the circumstances of vehicle mobileterminals.

[0112] The spread spectrum receiver according to the invention performsthe operation as shown in equations (2) (or (5)) and equation (3)employs a time division multiplexing correlator bank and thus obtainedcoherent channel evaluator as a core. Further, The receiver includes astate control unit (FSM_CONTROL) and a post correlation process unit.Furthermore, the receiver can execute initial PN synchronization, RAKEdiversity coherent combination, AFC and adjacent cell search andcombination receipt, and soft handoff,

[0113] Industry Practicability

[0114] 1) The spreading coherent receiver according to the inventionuses CDMA cellular system initial synchronization method based on amaximal energy window such that the RAKE receiver operates in themaximal energy window and improves the stability of acquiring initialsynchronization

[0115] 2) This invention uses a method for pilot channel tracking basedon multipath channel barycenter tracking loop. The receiver according tothe invention tracks multipath energy window, but not every delay path.Therefore, the stability of a spread spectrum receiver in multipathfading circumstances is improved and the hardware used in a spreadspectrum receiver is greatly reduced. For tracking N base stations, itis only necessary to establish N energy barycenter tracking loops.

[0116] 3) The spreading coherent receiver according to the inventionuses time division multiplexed correlator banks to search, therebygreatly increasing the search speed.

[0117] 4) The spreading coherent receiver according to the invention canaccomplish functions such as initial synchronization of the pilotchannel, track and channel evaluation, multipath maximal ratiocombination, AFC, cell search, hand-off, and macro-diversity.

[0118] 5) The design of the spreading coherent receiver according to theinvention can be described by using VHDL or Verilog languages,implemented by FPGA or ASIC. DSP core or external DSP chip is notnecessary in the spreading coherent receiver according to the invention.

[0119] Although embodiments of the present invention have been shown anddescribed, it will be understood by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

What is claimed is
 1. A direct spread spectrum/CDMA integrationspreading spectrum coherent receiver comprises: a state control meansfor receiving control information from a CPU (center processor unit),generating control information used for operating each of units,recording the operation states of each of units and reporting the CPU ofthe states; a timing generating unit for receiving a external clock,generating CPU interruption signals required for entire system, timingclock and time sequence by dividing frequency and counting, and foradjusting the timing based on a PN code tracking unit and the statecontrol unit; a correlator bank for performing effective correlatingintegration by time division multiplexing one complex correlator to formequivalent correlators; a post correlation data processing unit forreceiving the output from one of correlator in the correlator bank,processing the data included in the output from the correlator,performing initial acquisition, adjacent cell search, selection ofeffective multipath based on the energy window according to the controlsignals from the state control unit; a PN code tracking unit forreceiving a channel evaluation relating to effective multipath of pilotchannel from the post correlation data processing unit, calculating thebarycenter of a energy window and a loop filter to obtain a mode valuefor a variable mode counter, and sending the mode value to the timinggenerating unit to finely adjust the PN code generating clock, therebyadjusting local PN code phase; and an automatic frequency correction(AFC) loop calculating unit for performing frequency error evaluationand loop filter calculation based on the information associated witheffective multipath of the pilot channel from the post correlation dataprocessing unit, and sending the obtained result to a controllablefrequency reference unit.
 2. The direct spread spectrum/CDMA integrationspreading spectrum coherent receiver according to claim 1, wherein thestate control unit further comprises a CPU interface block, a receiverstate transformation control block, and a unit state control signalgenerating block, the state control unit interacts with the CPU, whichis controlled with baseband, of information, generates controlinformation used for operating state transformation of each of units,records the operation states of each of units and reports the CPU of thestates.
 3. The direct spread spectrum/CDMA integration spreadingspectrum coherent receiver according to claim 1, wherein the timinggenerating unit receives external clocks which are 16 times or 32 timesthe spread spectrum sequence chip rate.
 4. The direct spreadspectrum/CDMA integration spreading spectrum coherent receiver accordingto claim 1, wherein the correlator bank comprises four banks ofcorrelators, the correlators in each bank perform effective correlationintegration 31 times by time division multiplexing one complexcorrelator with 32 times the chip rate, thereby forming 31×4 equivalentcorrelators.
 5. The direct spread spectrum/CDMA integration spreadingspectrum coherent receiver according to claim 1, wherein furthercomprises a data delay line including random access memory (RAM) or Dflip-flop for four times sampling input data.
 6. The direct spreadspectrum/CDMA integration spreading spectrum coherent receiver accordingto claim 5, wherein the data delay line unit comprises four sets of RAM,which storage capacity is 18×6 bits, or D flip-flops, for outputting 72delay taps with ¼ chip interval, and sending output data to thecorrelator bank unit.
 7. The direct spread spectrum/CDMA integrationspreading spectrum coherent receiver according to claim 1, whereinfurther comprises a RAKE combining unit for receiving the channelvaluated results from the post correlation data processing unit anddecorrelating the data stream, and combining the effective multipathaccording to the control signals from the state control unit.
 8. Thedirect spread spectrum/CDMA integration spreading spectrum coherentreceiver according to claim 1, wherein further comprises a postcombining unit for receiving multipath combining results from RAKEcombining unit, and determining whether or not to performmacro-diversity of a plurality of base stations according to the controlsignals from state control unit, if macro-diversity is necessary, thepost-combining unit delays paths based on the time-delay difference ofrespective base stations provided by the CPU to align the paths to eachother in time, and performs macro-diversity of a plurality of basestations.
 9. The direct spread spectrum/CDMA integration spreadingspectrum coherent receiver according to claim 1, wherein furthercomprises a PN code generating and sliding unit for providing fivegroups of PN codes.
 10. The direct spread spectrum/CDMA integrationspreading spectrum coherent receiver according to claim 9, wherein threegroups of PN codes provided by the PN code generating and sliding unitare used for despreading data of three base stations, one of the restgroups of PN codes are used for searching adjacent cell, and the othergroup of PN codes are used for transmitter.
 11. The direct spreadspectrum/CDMA integration spreading spectrum coherent receiver accordingto claim 1, wherein further comprises a Walsh function generating unitwhich is controlled by the state control unit and the timing generatingunit for generating Walsh sequences depended on respective in andproviding generated Walsh sequences to the correlator bank unit.
 12. Thedirect spread spectrum/CDMA integration spreading spectrum coherentreceiver according to claim 8, wherein th macro-diversity comprises amacro-diversity preparing stage, a macro-diversity implementing stage,and a macro-diversity removing stage.